Certain subsurface conditions encountered during drilling operations can cause, or lead to, “loss of circulation,” or the loss of whole drilling fluid in quantity to the formation. Examples of such subsurface conditions include, for example: (1) natural or intrinsic fractures, (2) induced or created fractures; (3) cavernous formations (crevices and channels), and (4) unconsolidated or highly permeable formations (loose gravels).
Lost circulation materials are used to minimize loss of circulation. The lost circulation material forms a filter cake that effectively blocks voids in the formation. Lost circulation materials include fibrous materials, such as cedar bark and shredded cane stalk, flaky materials such as mica flakes, and granular materials such as ground limestone, wood, nut hulls, corncobs, and cotton hulls. U.S. Pat. No. 6,399,545 to Rose describes “tannin-containing organic waste products,” including “grape pomace, tomato pomace, beet pomace, yellow pine bark, yellow pine, wood bark and the like.” Rose, col. 2,II. 64-66.
Unfortunately, low electrical stability values have been reported for invert emulsion drilling fluids containing fibrous cellulosic lost circulation material. If the electrical stability value of a drilling fluid becomes too low, water wetting of solids occurs, which may cause the rheological properties of the fluid to break down, rendering the drilling fluid ineffective and even resulting in a shutdown of drilling operations. For example, Rose acknowledges that the “use of certain cellulose materials is known to ‘break’ emulsions.” Rose, col. 2, II. 11-12. Nevertheless, Rose does not describe a method for minimizing breaking of an emulsion type drilling fluid system comprising one or more fibrous lost circulation material.
Processes are needed to minimize breaking of emulsion type drilling fluid systems comprising one or more fibrous lost circulation material.